Report with 2 parts A (Chapter 1.1,1.2 etc.) + B (Chapter 1.1,1.2 etc.)

Question

I am trying to write a report which shuld contain two parts A + B. At the moment I have this:

What i would like to have is A instead of I , and B instead of II. and also that after B the first chapter should start again with 1. etc....

\documentclass[11pt, ngerman]{scrreprt}
\begin{document}

\begin{spacing}{1.2}
\part{This should be A.} 
\chapter{This should be 1.}
\section{This should be 1.1} 
\chapter{This should be 2.}
\section{This should be 2.1}
\part{This should be B.} 
\chapter{This should be 1.}
\section{This should be 1.1}

\chapter{This should be 2.}
\section{This should be 2.1} 
\end{document}